2010 Water Quality Monitoring Activities

-Medicine Lake-Twin Lake

Keith PilgrimBarr EngineeringMarch 17, 2011

brain huser is great

2010 Lake Water Quality Study for Medicine Lake

Long Term Monitoring Program Detect Long Term Trends in

Lake Water Quality… Land use changes BMP implementation In-lake activities Other, e.g. climate

What is Monitored Phosphorus Chlorophyll a Clarity (by Secchi disk) Basic lake characteristics Zooplankton Phytoplankton Aquatic plants

Medicine Lake

Medicine Lake (map)

Class: Level 1Size: 886 acMax Depth: 49 ftAverage Depth: 16 ftLittoral Area: 33% of total

Watershed:11,600 acLand use: commercial and residentialWater

Quality Monitoring Locations

Medicine LakeHistoric Data: Summer Averages

91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 100

10

20

30

40

50

60

70

80 Main Basin Total Phosphorus

Year

Tota

l Pho

spho

rus

(ug/

L)

Medicine LakeHistoric Data: Summer Averages

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 20100

10

20

30

40

50

60

70Main Basin Chlorophyll a

Year

Chl

orop

hyll

a (u

g/L)

Medicine LakeHistoric Data: Summer Averages

90 92 94 96 98 00 02 04 06 08 100.0

0.5

1.0

1.5

2.0

2.5

3.0Main Basin Clarity

Year

Secc

hi D

isc

(m)

Medicine Lake2010 Data Compared to State Standards

April May June July August September October0

102030405060708090

100110120 0

1

2

3

4

5

6

7

8

Main BasinC

once

ntra

tions

(µg/

L)

Secc

hi D

epth

(m)

Secchi Disc State Standard of > 1.4 m

SD

0102030405060708090

100110120 0

1

2

3

4

5

6

7

8

Main BasinC

once

ntra

tions

(µg/

L)

Secc

hi D

epth

(m)

Total Phosphorus State Standard of < 40 µg/L

Secchi Disc State Standard of > 1.4 m

SD

TP

April May June July August September October0

102030405060708090

100110120 0

1

2

3

4

5

6

7

8

Main BasinC

once

ntra

tions

(µg/

L)

Secc

hi D

epth

(m)

Chlorophyll a State Standard of <14 µg/L

Total Phosphorus State Standard of < 40 µg/L

Secchi Disc State Standard of > 1.4 m

SD

TPChl a

Medicine Lake2010 Data Compared to BCWMC Standards

April May June July August September October0

102030405060708090

100110120 0

1

2

3

4

5

6

7

8

Main BasinC

once

ntra

tions

(µg/

L)

Secc

hi D

epth

(m)

Chlorophyll a Goal of <10 µg/L

Total Phosphorus Goal of < 38 µg/L

Secchi Disc Goal of > 2.2 m

Chlorophyll a Goal of <10 µg/L

Total Phosphorus Goal of < 38 µg/L

SD

TP

Chl a

April May June July August September October0

102030405060708090

100110120 0

1

2

3

4

5

6

7

8

Main BasinC

once

ntra

tions

(µg/

L)

Secc

hi D

epth

(m)

Secchi Disc Goal of > 2.2 m

SD

April May June July August September October0

102030405060708090

100110120 0

1

2

3

4

5

6

7

8

Main BasinC

once

ntra

tions

(µg/

L)

Secc

hi D

epth

(m)

Total Phosphorus Goal of < 38 µg/L

Secchi Disc Goal of > 2.2 m

Total Phosphorus Goal of < 38 µg/L

SD

TP

Aquatic PlantsSpecies: 20+Tolerance: ModerateCoverage: Growth to 10 ftDensity: Low to mediumInvasives: Eurasian watermillfoil, curlyleaf pondweed

Potential Lake Changes with TMDL Implementation

Increased lake clarity Reduced blue-green algae

populations Increased aquatic plant coverage Increased dissolved oxygen

throughout the lake water column

If improved lake clarity, aquatic plant coverage, and dissolved oxygen, then improved habitat for aquatic life

Recommendations

Continued implementation of TMDL, BCWMC, and Plymouth Creek projects

Continued lake monitoring Document and track activities and

projects in the watershed that reduce phosphorus loading to Medicine Lake

Twin Lake Internal Phosphorus Loading Special

Investigation

Purpose of Study

Identify reasons for recent increases in

nutrients and algae in Twin Lake

Pertinent Twin Lake Characteristics

Surface area: 21 acres (small) Maximum depth: 54 feet (quite deep) Average depth: 25.7 Sheltered (protected from wind) Small, largely undeveloped watershed Connected to Sweeney Lake Strongly stratified Largely self contained, changes in water

quality and biota due to internal (non-watershed) processes.

Very low dissolved oxygen Nearly permanently low at depths below 16

feet Very high rate of phosphorus loading from

lake sediments (internal loading) during the summer and winter

Phytoplankton population now dominated by blue-green algae (cyanobacteria)

Pertinent Chemical and Biological Characteristics

Lake sediments are permanently oxygen depleted

Nearly all phosphorus deposited on sediment is re-released (nutrient cycling)

Spring mixing=phosphorus transport to lake surface

Fall mixing=phosphorus transport to lake surface

Phytoplankton levels may be influenced by: Zooplankton abundance Blue green algae upward mobility

What Is Affecting the Water Quality of Twin Lake?

Why Has Phosphorus Increased in Recent Years…

The lake is warmer, oxygen is lower for more of the lake

Management Options for Internal Load Control

Hypolimnetic withdrawl

Sediment phosphorus inactivation

Requires water inputs to replace water removed from lake bottom, several other drawbacks

Relatively inexpensive, can be effective on a long term basis for lakes with small watersheds

Management Options for Internal Load Control

Biomanipulation

Barley straw

Aeration

Innovative and natural way to control algae, appears to be occurring in Twin Lake already to some degree.Most often used for small lakes and ponds, can prevent algal growth in some cases, requires annual treatment.Can increase oxygen in lake water, however, may not stop internal loading and may transport phosphorus to the lake surface for algal growth

Management Options for Internal Load Control

Dredging Can reduce internal loading, primary drawback is high cost